Chorea is a movement disorder that results from basal ganglia injury due to a variety of causes in children. Chorea is characterized by sudden, brief, involuntary muscle contractions causing movements that appear to flow from body part to body part in an unpredictable manner. Disorders associated with chorea include CNS infections, post-infectious and other autoimmune diseases, ischemia during cardiopulmonary bypass, 'extrapyramidal' cerebral palsy, a variety of toxic and acute metabolic processes, degenerative conditions, and inborn errors of metabolism. In many cases the cause is unknown. In diseases with well defined neuropathology, chorea has been associated with abnormalities in the striatum (caudate and putamen) and the subthalamic nucleus (STN). However, the fundamental pathophysiology of chorea is not known. This is due in part to the lack of non-primate models and in part to the difficulty of measuring involuntary movements in the primate models that do exist. Current medical treatment options for chorea are few, may have significant side effects, and are often ineffective. The proposed experiments will develop quantitative 3-dimensional kinematic measures of chorea and use them measure spatial and temporal properties of chorea in adults and children with different disorders. Focal pharmacologic manipulation of basal ganglia nuclei will be used in monkeys to produce chorea. The resulting chorea will be measured in the monkeys and compared to human chorea in order to validate the monkey models, especially with respect to childhood chorea. The monkey models will then be used to investigate the fundamental pathophysiology of chorea by recording the activity of individual globus pallidus internal segment neurons before and during chorea. Through a combination of neurophysiologic and kinematic techniques to study experimentally produced chorea, the prevailing hypotheses of chorea pathophysiology can be tested rigorously. There is strong potential to identify the fundamental mechanisms of chorea. Development of a non-invasive method to quantify chorea in children and in monkeys will be an important advance toward better characterization of the pathophysiology of involuntary movements and development of more effective medical therapies.